1. Field of the Invention
The present invention relates to a centrifugal casting machine for manufacturing rotors, which are used in rotating appliances such as an electric motor and an electric generators, and more particularly to a centrifugal casting machine in which a lower mold applies a consistent pressure to a core to cause silicon steel plates constituting a core to be in close contact with each other during a centrifugal casting of rotors and in which the lower mold is movable up and down by means of a hydraulic ram to allow cast products to be easily taken out after the centrifugal casting operation.
2. Description of the Related Art
A rotating appliance such as an electric motor and an electric generator include a rotor and a stator as its substantial parts, in which the rotor is disposed at the center of the rotating appliance and the stator is installed in the rotating appliance to surround the rotor.
The rotor is composed of a plurality of stacked silicon steel plates which in turn constitute a core. The core is provided at upper and lower ends with end rings, and the upper and lower end rings are coupled to each other by means of a plurality of bars penetrating the core.
In order to manufacture such a rotor, a molten metal is vertically introduced from an upper end or a lower end of a mold to the opposite lower end or upper end thus molding an end ring, a core and a bar in a conventional technology. However, according to the conventional technology, cast defects are apt to be generated at the opposite side of a pouring gate and it is difficult to manufacture a large-sized rotor.
Considering the above problems, a centrifugal casting machine for casting rotors is used. An example of the centrifugal casting machine is disclosed in korean Unexamined Patent Publication No. 2011-0098020.
The centrifugal casting machine disclosed in the patent document includes an upper mold, a lower mold, a fixing part and a turntable.
The turntable is configured to rotate by means of a rotational force transmitted from a motor. The lower mold is fixedly installed on the turntable so as to define a molding space between a core disposed in the fixing part and the lower mold into which a molten metal is introduced to mold an end ring, and the upper mold is installed on an upper end of the fixing part so as to define a second molding space between the core and the upper mold into which a molten metal is introduced to mold an end ring.
At this point, the upper and lower molds are coupled to each other by means of a plurality of bolts with the fixing part disposed therebetween.
According to the conventional centrifugal casting machine, when the upper and lower molds are coupled to each other by means of bolts, silicon steel plates constituting a core are maintained in the close contact condition by pressure transmitted to the core from the upper and lower molds. However, since molding spaces for molding end rings are defined by the upper and lower molds, a pressure is not evenly transmitted to the core thus causing gaps to be partially generated between the silicon steel plates, and introduction of a molten metal into the gaps. In particular, for the upper mold, a pressure is concentrated in the center of the core via trim parts, and thus problems arise due to the creation of gaps between outer regions of the silicon steel plates.
Furthermore, when it is intended to mold rotors which have the same diameter but different lengths, the fixing parts stacked in the core and bolts for coupling the upper and lower molds must be replaced with different ones to construct a centrifugal casting machine having a different configuration, thus making the casting operation very cumbersome.
In addition, in order to take out the rotor in the fixing part after the casting of the rotor is finished, the rotor must be forcibly taken out of the fixing part using an additional device or tool after separation of the upper and lower molds, thus making the removal of cast products difficult.